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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station, 


URBANA,   APRIL,  1902. 


BULLETIN  NO.  71. 


EXPERIMENTS   WITH   INSECTICIDES   FOR  THE 
SAN  JOSE  SCALE. 


BY  S.  A.  FORBES,  STATE  ENTOMOLOGIST. 


The  "California  wash"  of  lime,  sulphur,  and  salt,  and  the 
"Oregon  wash"  of  lime,  sulphur,  and  blue  vitriol,  have  been  for 
many  years  the  general  reliance  of  the  fruit  growers  [of  the  Pa- 
cific Coas.t  for  protection  against  the  San  Jose  scale.  In  a  letter  to 
me  dated  October  22,  1901,  Prof.  C.  W.  Woodworth,  of  the  Ento- 
mological Department  of  the  University  of  California,  said  that 
"the  lime,  salt,  and  sulphur  mixture  is  the  sole  dependence  in  this 
state  for  killing  the  San  Jose  scale;"  and  under  the  same  date  Prof. 
A.  B.  Cordley,  of  the  Entomological  Department  of  the  Oregon 
Agricultural  College  and  Experiment  Station,  wrote:  "With  us 
the  lime,  salt,  and  sulphur  compound  is  a  very  satisfactory  remedy 
for  the  San  Jose  scale,  and  is  used  very  extensively.  In  fact,  this 

and  the  lime,  sulphur,   and  blue  vitriol  compound  are  practically 

241 


242  BULLETIN   NO.   71.  [April, 

the  only  ones  used  for  winter  sprays  for  this  insect.'1  As  early  as 
1889  the  California  wash  was  the  only  winter  remedy  recommended 
for  the  San  Jose  scale  by  the  Secretary  of  the  State  Board  of  Hor- 
ticulture, in  the  Annual  Report  of  the  Board  for  that  year;  and  in 
1896  Prof.  John  B.  Smith,  State  Entomologist  of  New  Jersey,  who 
visited  California  for  a  special  study  of  the  San  Jose  scale  and  its 
treatment  there,  found  the  lime,  salt,  and  sulphur  mixture  one  of 
the  "favorite  insecticides"  for  that  scale  in  California  and  on  the 
Pacific  Coast  generally.* 

The  introduction  of  these  insecticides  in  the  East  has  been 
long-  delayed,  probably  owing1  in  large  measure  to  unfavorable  re- 
ports of  experiments  made  in  the  Atlantic  states.  In  articles  pub- 
lished in  Bulletin  3  of  the  U.  S.  Division  of  Entomology,  issued  in 
1896,  and  in  Bulletin  30  of  the  same  series,  1901,  p.  34,  the  re- 
ported failure  of  the  California  wash  in  the  East  is  attributed 
to  the  frequent  occurrence  of  rains  shortly  after  the  insec- 
ticide had  been  applied,  and  chemical  testimony  is  brought  forward 
in  support  of  this  supposition. 

USE  OF  CALIFORNIA  AND  OREGON  WASHES  IN 
ILLINOIS. 

In  the  fall  of  1901,  when  an  appropriation  of  $15,000  for  in- 
secticide work  on  the  San  Jose  scale  became  available  to  my  office, 
I  was  embarrassed  by  the  fact  that  no  effective  insecticide  pre- 
viously used  by  us  had  been  found  free  from  serious  liability  to 
injure  the  more  tender  fruit  trees,  or  at  least  their  fruiting-  buds. 
The  peach  and  the  plum  were  especially  liable  to  serious  damag-e 
by  both  the  kerosene  sprays  and  the  whale-oil-soap  solution,  the 
first  being  injurious  to  the  tree,  and  the  second  very  commonly  de- 
structive to  the  fruit  buds  and,  of  course,  to  the  crop  of  the  follow- 
ing- year.  At  this  time  I  received  from  Professor  Cordley,  of 
Oreg-on,  the  above-mentioned  letter,  in  which  he  sugg-ested  that  I 
should  give  the  lime,  sulphur,  and  salt  compound  a  thorough  test 
in  Illinois,  and  further  said  that  in  Oregon,  where  this  mixture  is 
thoroughly  effective,  the  climate  is  as  moist  during-  the  winter — 
when  the  spray  is  principally  used — as  in  any  part  of  the  East. 
I  had  additional  testimony  to  the  same  effect  from  a  former 
student  and  assistant  of  mine,  Mr.  Fred  .McElfresh,  who  informed 
me,  after  a  year's  experience  in  'entomological  work  at  the  Oregon 
Agricultural  College,  that  the  weather  of  western  Oregon  is  very 
similar  to  that  of  the  greater  part  of  Illinois. 

*Rep.  Ent.  Dept.  N.  J.  Agr.  Exper.  Station,  1896,  p.  551. 


IQ02.]  EXPERIMENTS  WITH  INSECTICIDES  FOR  THE  SAN  JOSE  SCALE.  243 

Under  these  conditions  I  decided  last  fall  to  use  the  lime,  salt, 
and  sulphur  mixture,  standard  in  the  Pacific  states,  for  all  our  Illi- 
nois insecticide  work  on  the  peach  and  plum,  preferring  to  take  the 
risk  of  a  possible  inefficiency  of  the  insecticide  rather  than  the 
much  greater  one  of  serious  injury  to  the  orchard  tree.  The  sea- 
son seemed  favorable  to  the  treatment,  and  highly  encouraging  re- 
ports came  in  from  the  field  throughout  the  entire  winter  up  to 
early  March.  At  this  time,  in  order  to  secure  more  precise  and 
comprehensive  information  as  to  the  value  of  the  Oregon  and  Cali- 
nornia  washes,  I  detailed  one  of  my  office  assistants,  Mr.  E.  S.  G. 
Titus,  to  carry  out  a  series  of  experiments  with  them  under  various 
conditions,  and  sent  him  to  Sumerfield,  in  St.  Clair  county,  where 
he  remained  for  three  weeks,  supervising  the  treatment  of  the  trees, 
and  making  counts  of  scales  and  other  observations  of  the  results. 

SECONDARY  RESULTS  OF  THE  EXPERIMENTS. 

It  was  the  principal  object  of  these  experiments  to  test  the  ef- 
fects of  rains  on  the  two  washes  used,  but  other  important  results 
appeared  in  the  outcome  besides  those  immediately  aimed  at. 
Counts  of  dead  and  living  scales  on  the  check  trees  not  treated  and 
on  the  experimental  trees  before  treatment,  showed  a  surprising 
percentage  of  half-grown  scales  already  dead,  the  ratio  of  dead 
young  to  living  scales  varying  on  different  trees  and  on  different 
parts  of  the  same  tree  from  twenty-one  per  cent,  to  sixty-nine  per 
cent.  This  fact  had  already  been  observed  in  other  localities  where 
our  insecticide  work  was  in  progress,  and  had,  indeed,  been  noticed 
and  reported  as  early  as  1898  by  another  assistant  of  the  office,  Mr. 
E.  B.  Forbes,  engaged  in  distributing  to  infested  trees  in  southern 
Illinois  the  spores  of  a  fungus  parasite  of  the  San  Jose  scale. 

This  spontaneous  death  of  many  of  the  scales  which  might 
have  been  expected  to  pass  the  winter  alive,  was  apparently  due  in 
great  measure  and  in  both  instances  to  a  severe  drouth  of  the  pre- 
ceding year.  Consistently  with  this  explanation  the  dead  scales 
were  most  abundant  on  trees  worst  affected  by  the  drouth,  and  on 
parts  of  trees  to  which  the  flow  of  sap  would  naturally  be  least. 

Another  observation  of  importance  to  the  investigator  was 
made  with  reference  to  the  action  of  the  insecticide  in  loosening 
the  scales  of  the  insects  killed  by  it.  In  most  cases  where  the  ap- 
plication took  fatal  effect  the  scales  were  so  far  loosened  from  the 
bark  that  they  were  easily  rubbed  off,  and  might  be  washed  away  in 
large  numbers  by  an  ordinary  rain.  As  a  consequence,  if  counts  were 
made  of  dead  and  living  scales  upon  a  tree  before  treatment,  and 
again  after  a  treatment  and  after  a  heavy  rain  had  fallen,  the  ratio 


244  BULLETIN  xo.  ji.  [Apri/, 

of  living-  to  dead  might  be  as  great  in  the  latter  case  as  in 
the  former.  It  will  be  seen  that  by  overlooking-  this  circumstance 
an  investig-ator  might  easily  be  led  to  very  erroneous  conclu- 
sions as  to  the  effects  of  moisture  on  the  insecticide. 

GENERAL  FEATURES  OF  THE  EXPERIMENTS. 

The  actual  effect  of  rains  was  experimentally  ascertained  by 
heavily  spraying-  the  trees  with  water  at  selected  intervals  after 
treatment  with  the  wash,  and  by  making-  careful  counts  of  dead 
and  living-  scales  in  each  case  and  comparing-  the  ratios  so  arrived 
at  with  those  found  in  the  beginning-.  The  trees  sprayed  with 
each  mixture  were  treated  exactly  alike  except  as  to  the  subsequent 
application  of  water,  and  in  this  latter  respect  the  different  trees 
received  very  different  treatment.  Some,  for  example,  were  watered 
but  once,  and  that  the  next  day  after  the  application  of  the  insecti- 
cide wash;  and  others  were  watered  daily  for  the  seven  days  next 
following-  it.  In  order  to  avoid  interference  with  the  experiments 
by  rains,  which  fell  three  times  during-  the  fortnig-ht  covered  by 
the  greater  part  of  the  experiments,  some  of  the  trees  were  covered 
by  canvas  tents  at  night  and  whenever  rain  threatened. 

GENERAL  STATEMENT  OF  RESULTS. 

Details  of  all  forms  and  variations  of  the  experiment  will  be 
given  further  on,  but  it  is  sufficient  for  this  general  statement  to 
say  that  the  general  averag-e  result  of  a  single  spraying  of  twenty 
trees  with  lime,  sulphur,  and  salt  was  the  destruction  of  90.6  per 
cent,  of  the  scales  when  no  water  was  applied  within  five  days,  and 
of  86  per  cent,  when  water  was  used.  The  corresponding  result  of 
the  application  of  lime,  sulphur,  and  blue  vitriol  to  fifteen  trees, 
was  the  destruction  of  93  per  cent,  of  the  scales  without  water,  and 
92.2  per  cent,  when  water  was  applied  within  the  first  five  days. 

PERIOD  AND  METHODS  OF  THE  EXPERIMENTS. 

The  experiments  on  which  the  above  statement  rests  may  be 
conveniently  described  in  five  lots:  two  with  lime,  sulphur,  and 
blue  vitriol;  two  with  lime  sulphur  and  salt;  and  one,  a  special  ex- 
periment, with  both  these  washes  on  trees  covered  by  tents.  Two 
of  the  four  experiments  above  mentioned — one  with  the  California 
wash  and  one  with  the  Oregon  wash — were  begun  March  3,  and 
the  other  two  (in  which  also  both  washes  were  used)  were  begun 
March  5.  The  tent  experiment  was  begun  on  the  21st  of  the 
month.  Observations  on  all  the  lots  treated  were  continued  until 


I9O2.]          EXPERIMENTS   WITH    INSECTICIDES    FOR   THE    SAN   JOSE    SCALE.  24$ 

March  25;  that  is,  twenty-two  days  for  the  first  two  lots,  twenty 
days  for  the  third  and  fourth,  and  five  days  for  the  lot  under 
tents.  The  experiments  consisted  of  a  single  application  of  the 
insecticide  in  every  case,  with  varying1  subsequent  treatments  of 
the  different  trees  with  water.  Frequent  counts  of  dead  and  living- 
scales  were  made  for  all  of  the  trees,  no  attention  being  paid  in  these 
counts  to  old  scales,  outworn  and  dead,  but  only  to  those  whose 
size  and  immature  character  showed  that  they  belonged  to  the  new 
generation  of  the  preceding  fall.  Counts  of  dead  and  living  scales 
were  made  in  all  cases  either  before  or  shortly  after  the  applica- 
tion of  the  insecticide  spray.  It  was.  in  this  way  ascertained  that 
an  average  of  about  fifty  per  cent,  of  the  immature  scales  were  al- 
ready dead  on  these  trees  before  the  insecticide  was  applied;  and 
that  the  action  of  the  insecticide  was  scarcely  perceptible  within 
the  first  twenty-four  hours. 

EXPERIMENTAL  TREES  USED. 

Forty-three  trees  were  used  in  all  the  experiments,  twenty-five 
of  them  apple-trees  and  eighteen  -peach.  They  varied  in  height 
from  twelve  to  eighteen  feet;  in  spread  of  top  from  eight  to  twenty 
feet;  and  in  diameter  of  trunk  from  four  to  nine  inches.  The  av- 
erage height  was  fourteen  feet,  and  the  average  spread,  thirteen. 
The  general  condition  of  these  trees  varied  from  "very  poor"  to 
"excellent,"  six  of  them  being  described  as  "very  poor,"  eight,  as 
"poor,"  sixteen,  as  "fair,"  ten,  as  "good,"  and  three,  as  "excel- 
lent." Some  of  the  peach-trees  were  more  than  half  dead,  and 
many  of  them  in  such  a  condition  that  the  owners  were  about  to 
remove  them.  The  dry  weather  of  the  preceding  summer  had 
killed  the  young  growth  even  on  otherwise  healthy  trees,  and  in 
some  cases  much  of  the  older  wood  had  also  died  from  drouth.  All 
the  trees  were,  of  course,  infested  with  the  San  Jose  scale,  eight- 
een of  them  badly  so,  and  the  others  to  a  medium  degree. 

WEATHER  OF  THE  PERIOD. 

The  weather  of  the  experimental  period  was  the  ordinary 
variable  weather  of  an  Illinois  March,  the  temperature  at  seven 
o'clock  a.  m.  ranging  from  18°  F.,  on  the  18th,  to  54°,  on  the  15th, 
and  at  noon,  from  34°,  on  the  18th,  to  88°,  on  the  25th.  There  was 
an  unusual  amount  of  wind  from  the  southeast — on  not  less  than 
fourteen  days  out  of  the  twenty-two.  Rain  fell  on  six  days,  and  a 
light  snow  on  one  other.  The  first  rain,  on  March  7,  lasted  for 
two  and  a  half  hours,  but  was  very  light  — about  two  gallons  for 
each  experimental  tree  according  to  Mr.  Titus's  estimate.  The 


246  BULLETIN   NO.   Jl.  [April, 

temperature  at  the  time  was  56°.  On  the  ninth  day  after  the  begin- 
ning- of  the  first  experiment  (March  11)  the  weather  was  showery, 
with  heavy  mist  most  of  the  day,  the  temperature  60°  to  64°;  and 
on  the  thirteenth  day  (March  15)  a  heavy  shower  of  rain  fell,  with 
hail,  for  an  hour  in  the  afternoon,  amounting  to  ten  or  twelve  gal- 
lons to  the  tree.  The  17th  and  18th  were  cold — 26°  in  the 
morning  and  24°  at  noon  on  the  17th,  and  18°  in  the  morning  and 
24°  at  noon  on  the  18th.  The  wind  blew  strong  and  cold  from 
the  northwest,  with  a  light  snow  on  the  first  of  these  days.  A 
slow  drizzling  rain  fell  on  the  20tb,  beginning  at  about  five  in  the 
afternoon  and  continuing  through  the  night  and  all  the  following 
day. 

The  insecticide  sprays  were  applied  on  the  3d,  the  5th,  and 
the  20th.  March  3  was  a  partly  cloudy  day,  with  a  cold  raw  wind 
from  the  east  and  northeast,  the  thermometer  registering  30°  at  7 
a.  m.  and  40°  at  noon.  The  5th  was  a  clear  day,  with  a  northwest 
wind,  fairly  strong,  the  thermometer  30°  at  7  a.  m.  and  45'  at  noon. 
On  the  20th  the  wind  was  from  the  southeast,  with  a  threat  of 
storm  which  resulted  in  rain  at  five  o'clock  in  the  afternoon.  The 
temperature  was  34°  at  7  a.  m.  and  57°  at  noon. 

PREPARATION  OF  THE  INSECTICIDES. 

The  insecticide  washes  were  prepared  in  substantially  the 
same  manner.  For  the  California  wash,  fifteen  pounds  of  stone 
lime  were  slaked  in  a  little  very  hot  water,  fifteen  pounds  of  ground 
sulphur  being  slowly  poured  in  during  the  slaking  process  with 
constant  stirring  of  the  mixture.  This  was  then  boiled  for  an 
hour,  after  which  fifteen  pounds  of  salt  were  added  and  the  boil- 
ing continued  for  'fifteen  minutes  longer.  The  whole  was  then 
poured  into  a  barrel  through  a  strainer,  and  enough  boiling  water 
was  added  to  make  fifty  gallons.  In  the  preparation  of  the  Ore- 
gon wash  a  pound  and  a  quarter  of  blue  vitriol  was  used  instead 
of  the  salt,  the  crystals  of  the  blue  vitriol  being  dissolved  in  hot 
water  and  the  solution  added  slowly  to  the  slaking  lime.  The  ap- 
paratus used  was  a  Morrill  and  Morley  pump,  with  twenty-five 
'feet  of  hose  and  a  twelve-foot  extension  rod  with  a  double  Ver- 
morel  nozzle. 

THE  WATER  SPRAYS  TO  TEST  EFFECT  OF  RAINS. 

In  wetting  down  the  trees  to  imitate  the  effects  of  rain,  fifteen 
gallons  of  water  were  used  to  a  tree,  as  a  rule,  a  double  amount 
being  occasionally  applied  as  a  variation  of  the  experiment.  For 
a  tree  of  the  average  spread  of  thirteen  feet,  fifteen  gallons  of 


IQ02.]  EXPERIMENTS  WITH  INSECTICIDES  FOR  THE  SAN  JOSE  SCALE.  247 

water  was  equivalent  to  a  rainfall  of  a  sixth  of  an  inch,  amounting 
to  a  sharp  summer  shower.  The  washing-  and  leaching-  effect  of 
the  application  was,  however,  greater  than  that  of  a  correspond- 
ing shower,  since  the  water  spray  was  not  distributed  equally  over 
the  whole  area  covered  by  the  tree  top,  but  was  made  to  wet  the 
tree  equally  in  all  parts;  the  middle  part  of  the  tree  much  more 
freely,  consequently,  than  the  outer  parts.  It  would  doubtless  be 
fair  to  say  that  the  fifteen-gallon  portion  was  equivalent  in  effect 
on  the  average  experimental  tree  to  a  rainfall  of  a  third  of  an  inch, 
and  the  double  portion,  of  course,  to  twice  that  amount.  The 
time  taken  for  the  application  of  fifteen  g-allons  varied,  according 
to  the  weather  and  the  size  of  the  tree,  from  twenty  minutes  to 
thirty  or  thirty-five,  and  for  the  thirty-gallon  application  it  was 
never  less  than  an  hour.  The  water  in  all  cases  dripped  freely 
from  the  trees  for  some  time  after  spraying-  ceased,  carrying  with 
it  so  much  of  the  insecticide  in  solution  that  the  drip  was  of  about 
the  color  of  the  original  mixture. 

The  applications  of  water  were  varied  systematically  as  to 
number,  to  frequency,  and  to  period  of  time  between  the  insecti- 
cide operation  and  the  first  general  wetting1.  Tree  No.  1,  for  ex- 
ample, was  wet  every  day  for  a  week,  commencing-  the  next  day 
after  the  California  wash  was  applied;  tree  No.  2  was  wet  but 
once,  and  that  the  day  after  insecticide  treatment;  tree  No.  3  was 
sprayed  on  the  3d  with  the  California  wash,  and  with  water  on  the 
6th  and  every  other  day  thereafter  for  three  days;  tree  No.  6  was 
sprayed  but  once,  and  then  with  thirty  gallons  of  water  one  week 
after  insecticide  treatment;  and  tree  No.  9,  the  same,  except  that 
the  water  was  applied  at  the  end  of  two  weeks.  Further  particu- 
lars may  be  obtained  from  the  detailed  accounts  of  the  experi- 
ments. 

EXPLANATION  OF  TABLES. 

The  four  tables  in  the  text  have  been  prepared  to  present  in 
summary  form  the  detailed  results  of  the  treatment  for  each  tree 
as  shown  by  successive  counts  of  scales  on  selected  sample  twigs 
and  branches.  Ag-ainst  the  number  of  each  tree  is  placed  for  each 
date  on  which  special  observations  were  made,  the  number  of 
scales  counted  and  the  percentage  of  scales  killed  by  the  insecticide 
up  to  that  time.  The  first  count  shows  always  the  percentage  of 
scales  found  alive  at  the  time  of  treatment.  The  last  column  in 
each  table  shows  the  final  effect  of  treatment  in  the  form  of  a  gen- 
eral average  of  all  the  percentages  of  scales  killed,  excluding  only 
the  first  seven  days  subsequent  to  the  insecticide  treatment.  At 
the  bottom  of  each  table  is  a  series  of  data  for  the  entire  lot  of 


248  BULLETIN   NO.    Jl.  [April, 

trees,  corresponding-  in  form  to  those  given  in  the  body  of  the  table 
for  each  tree. 

EXPERIMENTAL  DETAILS. 
First  Lot  of  Trees.     California   Wash 

Nine  apple-trees  sprayed  with  lime,  sulphur,  and  salt  on  the  3d 
day  of  March.  Weather  partly  cloudy,  with  cold  raw  wind  from 
the  east-northeast;  temperature,  309  at  7  a.  m.  and  40°  at  noon. 

Dead  and  living-  scales  were  first  counted  on  these  trees  the 
following-  day,  March  4.  Although  the  fact  was  not  known  at  the 
time,  it  became  apparent  later  by  comparison  of  percentag-es  of 
scales  on  these  trees  with  those  found  on  check  trees  and  on  other 
lots  counted  before  insecticide  treatment  that  no  discoverable  effect 
of  the  insecticide  had  been  produced  at  the  time  this  first  count  was 
made.  If  any  scale  insects  had  been  killed  so  soon,  their  appear- 
ance had  not  yet  sufficiently  changed  to  indicate  the  fact.  The 
percentag-es  found  on  this  first  day  are,  consequently,  to  be  taken 
as  indicating-  the  ratio,  before  treatment,  of  dead  and  living- scales 
among-  the  young-  of  the  preceding  year.  One  thousand  three 
hundred  and  fifty  such  scales  were  counted  in  all,  and  52  per  cent, 
of  these  were  alive,  48  per  cent,  having  died  from  unknown  causes, 
in  most  cases  probably  from  drouth. 

In  determining-  the  effect  of  the  insecticide  under  the  varying- 
conditions  supplied,  this  first  count  of  living-  scales  was  made  the 
starting-  point  for  the  calculation  of  the  percentag-es  of  scales 
killed;  that  is,  if  only  50  per  cent,  of  the  scales  were  found  alive  at 
the  beginning-  of  the  experiment,  the  destruction  of  scales  by  the 
insecticide  was  figured  on  this  50  percent.,  those  dead  in  the  begin- 
ning- being-,  of  course,  ignored.  Counts  were  made  upon  carefully 
selected  specimen  twigs  or  branches,  the  number  counted  each  time 
varying-  from  100  to  400,  and  the  totals  for  each  tree,  from  300 
to  1,350.  The  total  number  of  scales  counted  from  this  lot  on  nine 
trees  was  9,000. 

The  effect  of  the  insecticide  was  only  gradually  made  mani- 
fest, and  was,  as  a  rule,  not  fully  produced  until  about  the  tenth 
day,  although  the  difference  between  the  final  result  and  that  ap- 
parent at  the  end  of  the  first  week  was  really  but  small.  Conse 
quently,  in  describing-  the  different  features  of  the  experiment,  the 
average  of  the  counts  after  the  first  week  will  be  taken  to  express 
the  final  effect  of  the  insecticide  in  destroying  the  San  Jose  scale. 
As  these  various  trees  were  treated  subsequent  to  the  insecti- 
cide spray  by  an  application  of  various  amounts  of  water  at  differ- 
ent intervals,  it  will  be  necessary  to  discuss  each  tree  separately. 


J9O2.]  EXPERIMENTS  WITH  INSECTICIDES  FOR  THE  SAN  JOSE   SCALE.  249 

LOT  I.    SPRAYED  WITH  LIME,  SULPHUR,  AND  SALT,  MARCH  3. 


<u 

e 

h 

Scales 

^ 

VO 

oo 

a 

0 

vn 

oo 

8 

S 

9 

3 

un 

M 

0 

as 

rt 

qj 

s 

a 

a 

s 

1 

c« 

0! 

5 

A 

OJ 

ns 
§ 

i 

2 

3 
5 
6 

7 

8 

9 
10 

No.  counted  .   .... 
Per  ct.  alive.  ..... 

150 

4° 

2OO 

400 

300 

200 

200 

350 

300 

1350 

Per  ct.  killed  

75 

IOO 

84 

83 

74 

IOO 

74 

IOO 

78 
300 

85 

IOO 

79 
600 

No.  counted  

150 

VJ 

Per  ct.  alive  

Per  ct.  killed  

78 

86 

95 

87 

92 
IOO 

90 
500 

No.  counted  

200 
2O 

150 

150 

IOO 

150 

Per  ct.  alive  

Per  ct.  killed  .    ... 

,- 

79 

89 

300 

88 

72 

IOO 

78 
550 

No.  counted  
Per  ct.  alive  

I50 
47 



150 

150 

Per  ct.  killed  

No.  counted  
Per  ct.  alive  

T 
64 

80 
150 

90 
150 

•  *  .  • 

91 

.... 

94 
150 

92 
300 

Per  ct.  killed  

81 

86 

86 

150 

86 
500 

No.  counted  
Per  ct.  alive  

150 

68 

ISO 

200 

150 

Per  ct.  killed  

80 

83 

89 

92 
150 

88 
450 

No.  counted  

IOO 

54 

IOO 

150 

150 

Per  ct.  alive  

Per  ct.  killed  ..'... 

14 

90 

81 

150 

88 
800 

No.  counted    

TOO 

200 

150 

300 

Per  ct.  alive  

56 

Per  ct.  killed  

8? 

87 
200 

85 

89 
250 

94 

150 

89 
600 

No.  counted  

150 

150 

— 

Per  ct.  alive  .    ... 

Per  ct.  killed 

77 

95 

.... 

99 

95 

92 

95 

J2  ^ 

•2  \ 

No.  counted  

1350 

C2 

700 

850 

45° 

650 

1400 

450 

700 

450 

650 

1350 

5650 

Per  ct  alive 

Per  ct.  killed  

67 

82 

86 

82 

87 

88 



92 

85 

83 

88 

86 

Tree  No.  /.—A  tree  sixteen  feet  high,  with  a  nine- inch  trunk 
and  a  twenty-foot  top;  in  fair  general  condition,  but  badly  infested 
with  the  San  Jose  scale.  After  insecticide  treatment  March  3, 
sprayed  with  fifteen  gallons  of  water  daily  for  seven  days,  from 
March  4  to  10  inclusive;  a  total  application  of  one  hundred  and  five 
gallons,  equal  to  about  half  an  inch  of  rainfall  over  the  whole  area 
beneath  the  tree  top.  Rains  falling,  as  above  described,  added 
about  fifteen  gallons  of  water  to  this  amount. 

Forty  per  cent,  of  the  young  scales  of  the  preceding  year  were 
alive  on  this  tree  when  the  treatment  began.  Three  days  after, 


2$0  BULLETIN   NO.   71.  [April, 

75  per  cent,  of  these  had  been  killed,  and  five  days  after,  84  per  cent. 
The  samples  taken  on  the  twelfth  and  nineteenth  days  showed  an 
extraordinary  percentage  of  living-  scales,— 26  per  cent,  on  each 
day, — and  the  average  final  ratio  of  scales  killed  stands  at  79  per 
cent. 

Tree  No.  2. — A  sixteen-foot  tree,  with  a  nine-inch  trunk  and 
an  eighteen-foot  top;  in  fair  general  condition,  but  badly  infested 
with  the  scale.  Treated  with  water  but  once,  and  that  on  March 
4,  the  day  succeeding  the  application  of  the  insecticide  spray. 
Rainfall  of  course  followed  on  the  7th,  llth,  and  15th,  as  on  all 
other  trees  of  this  experiment,  amounting  to  about  fifteen  gallons 
of  water  additional.  Thirty-seven  per  cent,  of  the  scales  alive  at 
the  time  of  treatment;  78  per  cent,  of  these  dead  three  days  after  ; 
and  86  per  cent,  dead  on  the  twelfth  day.  The  final  general  effect 
was  the  killing  of  90  per  cent,  of  the  scales. 

Tree  No.  j. — An  eighteen- foot  tree,  with  an  eight-inch  trunk 
and  a  thirteen-foot  top;  in  good  general  condition,  but  badly  in- 
fested. Water  treatment  three  days  after  the  insecticide  applica- 
tion, and  twice  on  alternate  days  thereafter,  making  forty-five 
gallons  of  water  thus  applied.  Twenty-nine  per  cent,  of  the  scales 
alive  when  the  treatment  began;  53  per  cent,  of  these  dead  on  the 
third  day  and  79  per  cent,  on  the  seventh;  the  average  final  destruc- 
tion of  scales,  78  per  cent. 

Tree  No.  5. — A  fifteen-foot  tree,  with  an  eight-inch  trunk  and 
an  eleven-foot  top;  in  poor  condition,  badly  infested.  Sprayed  with 
fifteen  gallons  of  water  five  days  after  treatment,  and  again  two 
days  later.  Forty-seven  per  cent,  of  the  scales  alive  in  the  begin- 
ning; 80  per  cent,  of  these  killed  by  the  sixth  day,  when  the  first 
count  was  made,  and  90  per  cent,  by  the  twelfth;  average  final  effect 
of  the  treatment,  the  destruction  of  92  per  cent,  of  the  scales. 

7m?  No.  6.  —  K  fifteen-foot  tree,  with  an  eight-inch  trunk  and 
a  twelve-foot  top;  in  poor  condition,  moderately  infested  by  the 
San  Jose  scale.  Treated  but  once  with  water,  and  this  on  the 
seventh  day  after  the  insecticide  spray,  when  thirty  gallons  were 
applied.  Sixty-four  per  cent,  of  the  scales  alive  in  the  beginning; 
84  per  cent,  of  these  dead  by  the  sixth  day  and  86  per  cent,  by  the 
twelfth;  average  ratio  of  scales  finally  killed,  86  per  cent. 

Tree  No.  7. — An  eighteen-foot  tree  with  an  eight-inch  trunk 
and  a  ten-foot  top;  in  poor  general  condition,  moderately  infested 
by  the  scale.  Fifteen  gallons  of  water  on  the  thirteenth  day  after 
insecticide  treatment,  and  another  fifteen  gallons  on  the  fourteenth; 
before  this,  only  the  rainfalls  already  described.  This  tree  and 
all  the  remaining  trees  of  this  lot  were  practically  check  trees 


JQ02.]  EXPERIMENTS  WITH  INSECTICIDES  FOR  THE  SAN  JOSE  SCALE.  251 

with  regard  to  the  effects  of  the  water  sprays,  since  these  were 
applied  after  the  full  effect  of  the  insecticide  must  have  been  pro- 
duced. Sixty-eight  per  cent,  of  the  scales  alive  in  the  beginning; 
80  per  cent,  of  these  dead  on  the  fifth  day  and  83  per  cent,  on  the 
seventh;  ratio  finally  killed,  88  per  cent. 

7rcc  No  8.-  -Seventeen  feet  high,  with  an  eight-inch  "trunk 
and  a  twelve-foot  top;  in  fair  general  condition,  but  badly  infested 
with  the  scale.  But  one  application  of  water,  and  that  fifteen 
gallons  on  the  fourteenth  day  after  insecticide  treatment.  Fifty- 
four  per  cent,  of  scales  alive  in  the  beginning,  and  54  per  cent,  of  these 
dead  on  the  third  day;  90  per  cent,  dead  on  the  sample  represent- 
ing the  fifteenth  day,  with  an  average  of  88  per  cent,  destroyed 
as  the  final  effect  of  the  insecticide. 

Tree  No.  9. — A  sixteen-foot  tree,  with  an  eight-inch  trunk  and 
an  eleven-foot  top;  in  fair  condition,  but  badly  infested.  No 
water  (except  rains)  until  the  fourteenth  day,  when  thirty  gallons 
were  applied.  Fifty-six  per  cent,  of  the  scales  alive  in  the  begin- 
ning; 83  per  cent,  of  these  dead  on  the  fifth  day  and  87  per  cent, 
on  the  twelfth;  average  final  effect,  89  per  cent,  destroyed. 

Tree  No.  10. — A  fifteen- foot  tree,  with  a  seven-inch  trunk  and  a 
thirteen-foot  top;  in  fair  condition,  moderately  infested.  No 
water  was  applied  to  this  tree,  and  the  effect  of  the  insecticide  was 
modified  only  by  the  natural  rainfall  already  referred  to.  Sixty- 
nine  per  cent,  of  the  scales  alive  in  the  beginning;  77  per  cent  of 
these  dead  on  the  third  day  and  95  per  cent,  on  the  sixth,  with  a 
final  average  result  of  95  per  cent,  destroyed. 

Taking  the  entire  group  of  nine  trees  together,  without  refer- 
ence to  differences  of  treatment  subsequent  to  the  insecticide  spray, 
it  appears  that  an  average  of  52  per  cent,  of  the  scales  were  alive 
in  the  beginning;  that  67  per  cent,  of  these  were  dead  by  the  third 
day,  82  per  cent,  by  the  fifth,  and  86  per  cent,  by  the  sixth;  and 
that  the  final  average  effect  of  the  treatment  was  the  destruction  of 
86  per  cent. 

Second  Lot  of  Trees.       California  Wash. 

Nine  trees,  partly  apple  and  partly  peach,  sprayed  with  lime, 
sulphur,  and  salt  on  the  5th  of  March.  Weather  clear,  with  fairly 
strong  northwest  wind  ;  temperature,  30°  at  7  a.  m.  and  45°  at 
noon.  In  this  case  the  dead  and  living  scales  were  counted  an 
sample  twigs  and  branches  from  a  part  of  the  trees  just  before  the 
application  of  the  insecticide,  and  from  another  part  on  the  fol- 
lowing day.  The  ratios  of  dead  to  living  scales  were  practically 
identical  in  these  two  lots,  thus  showing,  as  has  been  already 


252  BULLETIN   NO.   71.  [April, 

LOT  II.    SPRAYED  WITH  LIME,  SULPHUR,  AND  SALT,  MARCH  5. 


0 

£ 

H 

Scales 

U1 

t^ 

o 

o 

U1 

00 

0 
N 

r» 

N 
M 

CO 
N 

Tj- 

N 

tn 

N 

u-> 
N 

N 

V. 

a 

S 

u 

cti 

s 

u 

rt 

2 

03 

s 

« 

S 

a 
S 

a 

s 

rt 

s 

CS 

s 

rt 

s 

rt 

s 

ct 

5 

It 

'5 

4 
20 
27 
29 
31 
32 

33 
35 
36 

No.  counted  .  . 
Per  ct.  alive  .  . 

100 
A2 

2OO 

400 

2OO 

250 

850 

Per  ct.  killed.  . 

83 

8? 

80 

68 

100 

78 
25O 

No.  counted  .  . 

•7OO 

IW 

Per  ct.  alive  .  . 

47 

Per  ct.  killed.  . 

Q2 

08 

200 

95 

450 

No.  counted  .  . 
Per  ct.  alive  .  . 

2OO 
?6 

150 

300 

2t;o 

Per  ct  killed.  . 

62 
2OO 

80 

78 

88 
150 

83 

750 

No.  counted  .  . 
Per  ct.  alive  .  . 

200 
4.2 

— 

200 

200 



2OO 

Per  ct.  killed.. 

No.  counted  .  . 
Per  ct.  alive  .  . 

300 

-17 

.... 

80 

2OO 

ICO 

92 

.... 

87 
2^O 

98 

— 

93 

200 

93 
450 

Per  ct.  killed. 

78 
300 

83 

O2 

78 
300 

85 

IOOO 

No.  counted  .  . 

300 

300 



200 



2OO 

— 

Per  ct.  killed.. 

No.  counted  .  . 
Per  ct.  alive 

30O 
4C 

69 
2OO 

.... 

86 
300 

.... 

79 

2OO 

89 

.... 

87 
300 

85 

800 

Per  ct.  killed.. 

No.  counted  .  . 
Pet  ct.  alive 

2OO 
18 

20O 

70 

200 

80 

300 

.... 

300 

87 

.    •    •   • 

2OO 

95 
300 

87 

IIOO 

Per  ct.  killed.. 

No.  counted  .  . 
Per  ct.  alive  . 

2OO 

;  I 

62 
300 

00 
2OO 

:: 

00 
200 

99 

.... 

.... 

91 

200 

97 
200 

94 
600 

Per  ct.  killed.  . 

51 

.... 

85 

.... 

97 

.... 

.... 

94 

99 

97 

—  ^ 

5 

0    I 

H  ) 

No.  counted  .  . 
Per  ct.  alive  .  . 

2OOO 
42 

500 

IO5C 

IOOO 

1200 

650 

700 

500 

400 

400 

400 

20OO 

6250 

Per  ct.  killed.  . 

56 

71 

84 

86 

93 

86 

88 

84 

94 

93 

89 

89 

remarked,  that  scales  kil  led  the  first  day,  if  any,  do  not  sufficient- 
ly change  in  appearance  within  that  time  to  suggest  the  fact. 
Subsequent  counts  of  scales  were  made  for  this  lot  on  eleven  later 
dates,  the  number  counted,  as  before,  ranging  from  one  hundred  to 
four  hundred,  and  amounting  for  the  lot  to  10,500  specimens. 

Tree  No.  4. — An  apple-tree,  sixteen  feet  high,  with  a  nine-inch 
trunk  and  a  twelve-foot  top  ;  in  fair  condition,  but  badly  infested 
by  the  scale.  This  tree  received  but  one  water  treatment,  and  that 
on  the  7th  of  March,  two  days  after  the  insecticide  application  and 
on  the  same  day  as  the  first  light  fall  of  rain.  Fifteen  gallons 


1 902.]         "EXPERIMENTS  WITH  INSECTICIDES  FOR  THE  SAN  JOSE    SCALE.  253 

were  applied,  and  approximately  two  gallons  must  be  added  for  the 
rainfall.  Scales  alive  in  the  beginning1,  42  per  cent.  ;  83  per  cent, 
of  these  killed  on  the  sample  for  the  fifth  day,  with  an  average  of  78 
per  cent,  as  the  final  effect  of  the  insecticide. 

Tree  No.  20. — A  peach-tree,  twelve  feet  high,  with  a  six-inch 
trunk  and  a  nine-foot  spread  of  top  ;  in  very  poor  condition,  though 
but  moderately  infested  by  the  scale.  No  water  except  the  natural 
rainfall.  Forty-seven  per  cent,  of  the  scales  were  alive  in  the  be- 
ginning ;  92  per  cent,  of  these  were  dead  on  the  thirteenth  day, 
when  the  first  subsequent  count  was  made,  and  98  per  cent,  on  the 
sample  for  the  twentieth  day,  the  final  average  effect  being  reckoned 
at  95  per  cent,  destroyed. 

7"rce  No.  27. — An  apple-tree,  fifteen  feet  high,  with  an  eight- 
inch  trunk  and  a  seventeen-foot  top  ;  in  good  condition,  moderately 
infested  with  the  scale.  This  tree  was  sprayed  with  water  but 
once,  and  that  five  days  after  the  insecticide  application.  Thirty- 
six  per  cent,  of  the  scales  were  alive  in  the  beginning;  62  per  cent, 
of  these  were  dead  on  the  fourth  day  and  80  per  cent,  on  the  fifth, 
the  average  final  effect  being  reckoned  at  83  per  cent,  destroyed. 

Tree  No.  29. — An  apple-tree,  twelve  feet  high,  with  a  seven- 
inch  trunk  and  a  fifteen-foot  top  ;  in  bad  condition,  and  heavily  in- 
fested. Twice  treated  with  water,  once  on  the  fifth  day  after  the  insec- 
ticide spray  and  once  on  the  tenth,  in  each  case  with  fifteen  gallons. 
Forty-two  per  cent,  of  the  scales  alive  at  the  beginning  of  the  exper- 
iment; 80  per  cent,  of  these  dead  on  the.fourth  day  and  92  per  cent, 
on  the  tenth  day  ;  the  average  final  effect,  the  destruction  of  93 
per  cent,  of  the  scales. 

Tree  No.  j/. — AD  apple-tree,  twelve  feet  high,  with  an  eight- 
inch  trunk  and  a  nineteen-foot  top;  in  good  general  condition,  and 
moderately  infested  by  the  scale.  Once  treated  with  thirty  gallons 
of  water,  on  the  next  day  after  the  application  of  the  insecticide 
spray.  Thirty-seven  per  cent,  of  the  scales  were  alive  in  the  be- 
ginning ;  78  per  cent,  of  these  were  dead  on  the  fourth  day  and  83 
per  cent,  on  the  fifth;  the  final  average  effect  of  the  insecticide,  85 
per  cent,  destroyed. 

Tree  No.  J2.—A  peach-tree,  twelve  feet  high,  with  a  six-inch 
trunk  and  a  nine-foot  top  ;  in  fair  general  condition,  but  heavily 
infested.  Treated  with  fifteen  gallons  of  water  a  day  for  three 
days  in  succession,  beginning  the  next  day  after  the  insecticide 
spray  was  applied.  The  second  of  these  treatments  coincided  with 
the  first  day's  rain.  Forty- four  per  cent,  of  living  scales  at  the  be- 
ginning ;  69  per  cent,  of  these  dead  on  the  fourth  day  and  86  per 


254  BULLETIN    NO.   71.  [April, 

cent,  on  the  tenth,  according-  to  the  sample  for  that  day  ;  the  final 
average  effect,  the  destruction  of  85  per  cent. 

Tree  No.  jj — A  peach-tree,  nine  feet  high,  with  a  three-inch 
trunk  and  an  eight-foot  top  ;  in  good  condition,  moderately  infested 
by  the  scale.  Sprayed  twice  in  succession  with  fifteen  gallons  a 
day,  following-  immediately  upon  the  insecticide  treatment,  the 
second  application  coinciding-  with  the  first  day's  rain.  Forty- 
five  per  cent,  of  the  scales  alive  at  the  start;  70  per  cent,  of  these 
dead  on  the  fourth  day  and  80  per  cent,  on  the  tenth;  final  averag-e 
effect,  the  destruction  of  87  per  cent,  of  the  scales. 

Tree  No.  jj. — A  peach-tree,  fifteen  feet  hig-h,  with  five-inch 
trunk  and  a  twelve-foot  top;  in  poor  condition,  and  moderately  in- 
fested by  the  scale.  Treated  but  once  with  water,  and  that  on  the 
tenth  day  after  the  experiment  began,  this  treatment  coinciding 
with  the  third  day's  rain.  Thirty-eight  per  cent,  of  the  scales 
alive  at  the  time  of  the  application  of  the  insecticide;  62  per  cent, 
of  these  dead  on  the  second  day  and  90  per  cent,  on  the  fifth,  with 
an  average  final  destruction  of  94  per  cent,  of  the  scales. 

Tree  No.  36. — A  peach-tree,  fifteen  feet  high,  with  a  six-inch 
trunk  and  an  eight-foot  top;  in  poor  condition,  and  heavily  infested. 
Treated  with  water  twice,  once  on  the  day  following  the  insecti- 
cide treatment  and  once  on  the  tenth  day  of  the  experiment,  the 
last  treatment  coinciding  with  the  third  day  of  rain.  Fifty-one 
per  cent,  of  the  scales  alive  in  the  beginning,  and  51  per  cent, 
of  these  dead  on  the  second  day  after  insecticide  treatment;  85 
per  cent,  dead  on  the  fifth  day,  with  a  final  average  destruction  of 
97  per  cent,  of  the  scales. 

Taking  this  group  of  nine  trees  as  a  whole  and  averaging  all 
statements  concerning  them,  it  appears  that  42  per  cent,  of  the 
scales  were  alive  when  the  experiment  began;  that  56  per  cent,  of 
these  had  been  killed  by  the  treatment  by  the  second  day  thereafter, 
71  per  cent,  by  the  fourth  and  84  per  cent,  by  the  fifth;  and  that 
the  final  average  effect  was  approximately  89  per  cent,  destroyed. 

To  this  lot  it  will  be  convenient  to  add  for  discussion  two 
other  trees  sprayed  with  lime,  sulphur,  and  salt  on  the  7th  of 
March,  which,  it  will  be  remembered,  was  the  day  of  the  first 
rainfall  occurring  in  the  experimental  period.  These  trees  re- 
ceived no  water  treatment,  but  were  intended  as  checks  on  the 
other  experiments. 

Tree  No.  38. — The  first  of  these  was  a  peach-tree,  nine  feet 
high,  with  a  five-inch  trunk  and  a  ten-foot  top.  It  was  in  excel- 
lent condition,  and  only  moderately  infested.  Thirty-eight  per 
cent,  of  the  scales  were  alive  on  the  day  preceding  the  insecticide 


1902.]          EXPERIMENTS  WITH  INSECTICIDES   FOR  THE  SAN  JOSE  SCALE.  255 

application,  and  on  the  day  following1  the  treatment  31  per  cent, 
of  these  were  dead.  No  other  count  was  made  upon  this  tree  until 
the  eleventh  day,  when  96  per  cent,  appeared  to  have  been  killed. 
The  final  general  effect  was  an  average  of  89  per  cent,  of  the  scales 
destroyed. 

Tree  No,  jg. — The  second  tree  of  this  pair  was  also  a  peach- 
tree,  about  nine  feet  high,  with  a  five-inch  trunk  and  a  ten-foot 
top.  It  was  in  excellent  general  condition,  and  moderately  in- 
fested. Only  27  per  cent,  of  the  scales  were  alive  when  the  experi- 
ment began  ;  29  per  cent,  of  these  were  dead  by  the  second  day 
after  treatment  and  84  per  cent,  by  the  third  day  ;  and  the  gen- 
eral final  effect  averaged  91  per  cent,  of  the  scales  destroyed. 

GENERAL  RESULTS  OF  EXPERIMENTS  WITH  LIME, SULPHUR,  AND  SALT. 

An  analysis  of  the  data  contained  in  the  above  descriptions  of 
Lots  1  and  2  and  in  the  tables  of  percentages  for  those  lots  ena- 
bles us  to  distinguish  two  groups  of  trees  ;  those  which  received 
some  treatment  of  water  within  five  days  after  the  insecticide  ap- 
plication, and  those  which,  if  treated  with  water  at  all,  did  not 
receive  it  until  the  principal  effect  of  the  insecticide  had  already 
been  produced.  There  are  eleven  trees  in  the  first  group,  namely, 
1,  2,  3,  4,  5,  27,  29,  31,  32,  33,  and  36,  and  nine  trees  in  the  second, 
namely,  6,  7,  8,  9,  10,  20,  35,  38,  and  39. 

The  average  final  effect  of  the  insecticide  upon  the  nine  trees 
of  the  second  group  was  the  destruction  of  90.6  per  cent,  of  the 
scales,  and  the  corresponding  destruction  on  the  eleven  trees  of  the 
first  group  was  86.1  per  cent.,  making  a  difference  of  4.5  per  cent, 
due  to  the  action  of  water  on  the  insecticide  when  applied  within 
five  days  after  the  original  treatment.  In  other  words  and  more 
generally  stated,  it  may  be  said  that  in  these  experiments  the 
effect  of  thoroughly  watering  the  treated  tree  during  the  first  five 
days  after  the  experiment  began,  was  to  diminish  the  destructive 
effect  of  the  insecticide  by  approximately  5  per  cent. 

If,  regardless  of  this  difference,  we  take  these  twenty  trees  as 
a  group,  we  find  that  48  per  cent,  of  the  young  scales  of  the  pre- 
ceding year  were  dead  when  the  experiment  began  ;  and  that  43 
per  cent,  of  these  were  killed  by  the  second  day  after  treatment, 
60  per  cent,  by  the  third,  84  per  cent,  by  the  fifth,  and  86  per  cent, 
by  the  sixth.  The  average  effect  of  the  insecticide,  as  shown  by 
counts  made  from  the  seventh  to  the  twenty-second  day,  amounted 
to  88.4  per  cent.;  or,  if  we  include  only  the  counts  from  the  tenth  to 
the  twenty-second  day,  it  stands  at  89  per  cent. 


256  BULLETIN   NO.   J\.  [April, 

LOT  III.    SPRAYED  WITH  LIME,  SULPHUR,  AND  BLUE  VITRIOL,  MARCH  3. 


il 

<u 

h 

Scales 

**• 

vO  . 

oo 

o- 

0 

U~l 

oo 

o 

M 

r» 

N 

ro 
N 

vn 
M 

iy» 

M 

0 

ts 

S 

« 

5 

n) 
£ 

o! 

s 

a 

s 

rt 

% 

rt 

s 

cd 

S 

<B 
g 

ct 
g 

CS 

s 

S 
§ 

ii 

12 
13 
14 

15 
16 

17 

No.  counted  

3oo 
6? 

300 

150 

150 

150 



250 

150 

850 

Per  ct.  alive  

Per  ct.  killed  . 

8; 

93 
250 

93 
3°o 

92 

250 

•    •    .    * 

88 

98 

2OO 

93 

IOOO 

No.  counted  

300 

66 

300 

Per  ct.  alive  

Per  ct.  killed  

8r 

93 
250 

06 
250 

350 

95 



300 

95 

300 

95 
1450 

No.  counted  

200 

Per  ct.  alive  

57 

Per  ct.  killed  

89 
150 

94 

95 

96 

IOO 

98 
150 

94 
600 

No.  counted  
Per  ct.  alive 

300 
4Q 

150 



200 

Per  ct.  killed  

No.  counted  
Per  ct.  alive    

300 
fil 

83 

150 

.... 

96 
200 

150 

IOO 

93 



84 

06 
250 

92 
700 

Per  ct.  killed  

87 

80 

81 

300 

97 

98 
300 

89 
1300 

No.  counted  
Per  ct  alive 

30O 
1* 

300 

300 

400 

Per  ct.  killed  
No.  counted  

300 
41 

2OO 

81 

150 

92 
300 

93 
150 

.    .    •    . 

94 

95 

150 

93 
600 

Per  ct.  alive  

Per  ct.  killed  

68 

76 

95 

90 

.... 

99 

95 

-   ( 

s  } 
£l 

No.  counted  

2IOO    800'   6OO 
56  

150 

lOoO 

1450 

450 

1050 

1050 

1500 

6500 

Per  ct.  alive  

Per  ct.  killed  

79     84 

76 

00 

92 

96 

93 

90 

97 

93 

77it'rd  Lot  of  Trees.     Oregon  Wash. 

This  lot  of  experimental  trees  corresponds  to  the  first  in  all 
particulars  except  that  the  Oregon  wash  of  lime,  sulphur, and  blue 
vitriol  was  used  as  an  insecticide  instead  of  the  California  wash, 
and  that  the  experiment  was  made  with  seven  trees  instead  of  nine. 
The  variations  in  treatment  omitted  in  this  lot  correspond  to  those 
of  Nos.  5  and  7  of  L/ot  1.  All  were  apple-trees,  growing  in 
the  same  orchard  as  those  of  the  first  lot. 

Tree  No.  //. — An  eighteen-foot  tree,  with  an  eight-inch  trunk 
and  a  twelve-foot  spread;  in  excellent  condition,  and  moderately 
infested.  Sprayed  with  fifteen  gallons  of  water  daily  for  seven 
days,  beginning  March  4,  the  next  day  after  insecticide  treatment. 
Sixty-seven  per  cent,  of  the  scales  alive  at  the  beginning  of  the 
experiment;  85  per  cent,  of  these  dead  on  the  third  day  and  93  per 


I9O2.J          EXPERIMENTS  WITH  INSECTICIDES  FOR  THE  SAN  JOSE  SCALE.  257 

cent,  on  the  seventh  ;  the  average  final  effect  of  the  insecticide,  the 
destruction  of  93  per  cent,  of  the  scales.  Comparison  with  No.  1— 
similarly  treated  except  that  the  California  wash  was  used — shows 
a  difference  of  14  per  cent,  of  the  scales  finally  killed,  in  favor  of 
the  Oregon  wash. 

Tree  Xo.  12. — A  fifteen-foot  tree,  with  an  eight-inch  trunk  and 
a  twelve-foot  top;  in  fair  condition,  moderately  infested  with  the 
scale.  Sprayed  but  once,  with  fifteen  gallons  of  water,  on  the  day 
following  the  insecticide  treatment.  Sixty-six  per  cent,  of  the 
scales  alive  in  the  beginning;  85  per  cent,  of  these  dead  by  the 
third  day  ;  93  per  cent,  by  the  seventh,  and  96  per  cent,  by  the 
sample,  on  the  twelfth  ;  the  average  final  effect,  the  destruction  of 
95  per  cent.  Comparison  with  No.  2,  the  corresponding  specimen 
of  Lot  1,  gives  a  difference  in  favor  of  the  Oregon,  wash  amount- 
ing to  5  per  cent,  of  scales  finally  killed. 

Tree  No.  ij. — A  twelve-foot  tree,  with  a  six-inch  trunk  and  a 
thirteen-foot  top;  in  good  condition,  and  but  moderately  infested. 
Sprayed  with  water  three  times,  beginning  March  6,  with  inter- 
vals of  one  day  between  applications,  the  first  rainfall  coming  be- 
tween the  first  and  second  sprayings.  Fifty-seven  per  cent,  of  the 
scales  alive  in  the  beginning;  89  per  cent,  of  these  dead  on  the 
seventh  day,  when  the  first  subsequent  count  was  made,  and  94 
per  cent,  on  the  twelfth  ;  general  average  effect,  the  destruction 
of  94  per  cent.  On  the  companion  tree,  No.  3  of  the  first  lot,  an 
average  final  destruction  of  78  per  cent.,  making  a  difference  of  16 
per  cent,  in  favor  of  the  Oregon  wash. 

Tree  No.  14. — This  tree  was  thirteen  feet  high,  with  a  six- 
inch  trunk  and  a  sixteen-foot  top.  It  was  in  good  condition  but 
badly  infested  by  the  scale.  It  was  treated  but  once  with  water, 
thirty  gallons  being  applied  seven  days  after  the  insecticide,  agree- 
ing in  this  respect  with  No.  6  of  Lot  1.  Forty-nine  per  cent, 
of  the  scales  were  alive  in  the  beginning.  Eighty-three  per  cent, 
of  these  had  been  killed  by  the  fifth  day,  and,  according  to  the 
sample  count  made,  96  per  cent,  by  the  seventh  day.  Owing,  how- 
ever, to  a  low  ratio  in  the  hundred-scales  count  on  the  twentieth 
day,  the  final  effect  stands  at  92  per  cent,  of  the  scales  destroyed. 
The  corresponding  ratio  for  No.  6  was  86  per  cent. — a  difference  of 
6  per  cent. ,  in  this  case,  in  favor  of  the  Oregon  wash. 

Tree  No.  75 . — A  thirteen-foot  tree,  with  a  six-inch  trunk  and 
an  eighteen-foot  top;  in  fair  condition,  but  badly  infested  by  the 
scale.  This  tree  received  no  treatment  with  water  until  March  17, 
when  15  gallons  were  applied — fourteen  days  after  the  applica- 
tion of  the  insecticide.  Tree  No.  8  of  Lot  1  is  the  companion  tree. 


258 


BULLETIN    NO.   Jl. 


{April, 


Sixty-one  per  cent,  of  the  scales  on  No.  15  were  alive  in  the  be- 
ginning- ;  87  per  cent,  of  these  were  dead  on  the  fifth  day  ;  and 
the  final  average  stands  at  89  per  cent.  This  agrees  practically 
with  the  average  for  No.  8,  which  was  88  per  cent. 

Tree  No.  16.—  A  fifteen-foot  tree,  with  an  eight-inch  trunk  and 
a  fifteen-foot  top;  in  fair  condition,  but  badly  infested.  This  tree 
received  no  water  treatment  until  the  fourteenth  day,  when  thirty 
gallons  were  applied.  Forty-eight  per  cent,  of  the  scales  alive 

LOT  IV.    SPRAYED  WITH  LIME,  SULPHUR,  AND  BLUE  VITRIOL,  MARCH  5. 


<L> 
<U 

H 

Scales 

U~l 

t-^ 

O 

p 

u-> 

oo 

o 

N 

N 

N 

P4 

rn 
N 

-t- 

M 

u-i 
0» 

1/1 
N 

(S 

« 

§ 

a 
% 

rt 

% 

03 

s 

ct 

2 

a) 

5 

Rt 

E 

c9 

§ 

a 

S  • 

n 

§ 

a 

& 

tt 

& 

a 

2 

18 

21 

23 
24 
26 
28 
30 
22 

No.  counted  .  . 
Per  ct.  alive  .  . 

300 

47 

200 

.  300 

400 

300 

.... 

200 

200 

1  100- 

Per  ct.  killed  . 

No.  counted  .  . 
Per  ct.  alive  .  . 

100 
•?! 

15 

IOO 

83 

IOO 

89 
150 

150 

87 

91 

87 
2OO 

88 
500 

Per  ct.  killed  . 

No.  counted  .  . 
Per  ct.  alive  .  . 

300 
40 

o 

300 

90 

98 

96 
200 

97 
300 

97 
800 

300 

Per  ct.  killed  . 

No.  counted  .  . 
Per  ct.  alive 

6q 

88 

02 

88 

20O 

89 

550 

2OO 
4.2 

206 

200 

150 

200 

Per  ct.  killed  . 

No.  counted  .  . 
Per  ct.  alive 

300 
•j-l 

38 

2OO 

200 

92 
2OO 

92 

300 

00 

300 

96 
2OO 

93 
800 

Per  ct.  killed  . 

No.  counted  .  . 
Per  ct  alive 

250 

eg 

35 

68 

84 

150 

2OO 

93 
200 

97 

87 
2OO 

92 
600 

Per  ct.  killed  . 

No.  counted  .  . 
Per  ct.  alive 

76 
300 

91 

oo 

83 

3OO 

9i 

IOOO 

200 

AA 



200 

200 

300 

Per  ct.  killed  . 

No.  counted  .  . 
Per  ct.  alive 

300 
AA 

92 
3OO 

86 
300 

.... 

83 
200 

93 
150 

92 
2OO 

89 

850 

Per  ct.  killed  . 

88 

00 

98 

•  •  •  • 

94 

98 

95 

-   ( 
«  } 

0    ) 

H  ( 

No.  counted  .  . 
Per  ct  alive 

1950 

AA 

700 

500 

1550 

750- 

IOOO 

800 

400 

500 

950 

I800 

6200 

Per  ct.  killed  . 

22 

66 

86 

93 

90 

93 

91 

9i 

94 

91 

9i 

March  4;  81  per  cent,  of  these  dead  on  the  fifth  day  and  92  per 
cent,  on  the  twelfth,  with  a  general  final  average  of  93  per  cent, 
destroyed.  The  corresponding  tree  of  the  other  lot  is  No.  9,  which 
shows  a  final  average  destruction  of  89  per  cent. 


1902.]  EXPERIMENTS  WITH  INSECTICIDES  FOR  THE  SAN  JOSE  SCALE.  259 

Tree  No.  77. — An  eighteen-foot  tree,  with  a  nine-inch  trunk 
and  an  eighteen-foot  top;  in  poor  condition,  and  badly  infested. 
A  check  tree,  receiving1  no  water  treatment,  the  effect  of  the  insec- 
ticide being-  consequently  modified  only  by  the  three  rains  de- 
scribed. Forty-one  per  cent,  of  the  scales  alive  in  the  beginning1; 
68  per  cent,  of  these  dead  in  three  days  and  95  per  cent,  in  twelve, 
with  a  general  average  of  95  per  cent,  finally  destroyed.  This,  it 
will  be  noticed,  is  the  same  final  average  result  as  that  of  the  com- 
panion experimental  tree,  No.  10. 

Fourth  Lot  of  Trees.     Oregon  Wash. 

This  lot  is  essentially  a  duplicate  of  Lot  2  except  with  re- 
spect to  the  insecticide  treatment,  which  was  identical  with  that 
of  Lot  3,  and  also  with  respect  to  the  number  of  trees  made  use  of, 
which  was  eight  in  this  lot  and  nine  in  Lot  2.  All  variations  of 
experiments  with  Lot  2  are  represented  in  Lot  4  with  the  exception 
of  that  for  No.  29. 

Tree  No.  18. — A  sixteen-foot  apple-tree,  with  a  nine-inch  trunk 
and  a  twenty-foot  top;  in  fair  general  condition,  but  badly  infested 
by  the  scale.  Treated,  like  No.  4  of  Lot  2,  with  a  single  applica- 
tion of  fifteen  gallons  of  water  on  the  second  day  after  the  experi- 
ment, coinciding  with  the  first  shower  of  rain.  Forty-seven  per 
cent,  of  the  scales  alive  when  the  insecticide  was  applied;  15  per 
cent,  of  these  dead  on  the  second  day  and  83  per  cent,  on  the  fifth, 
with  a  final  average  destruction  of  88  per  cent.  The  correspond- 
ing ratio  for  the  companion  tree,  No.  4,  was  80  per  cent. 

Tree  No.  21. — A  fifteen-foot  peach-tree,  with  an  eight-inch 
trunk  and  an  eighteen-foot  top;  in  good  condition,  and  but  moder- 
ately infested,  This  received  the  same  water  treatment  as  No.  27 
of  Lot  3,  namely,  one  application  of  fifteen  gallons  of  water  on  the 
fifth  day  after  the  insecticide.  Thirty-one  per  cent,  of  the  scales 
were  alive  in  the  beginning.  None  of  them  appeared  to  have  been 
killed  on  the  second  day  thereafter,  but  90  per  cent,  of  these  were 
dead  on  the  fifth  day,  and  98  per  cent.,  according  to  the  count  made, 
five  days  thereafter.  The  general  final  average  was  97  per  cent, 
destroyed.  The  corresponding  ratio  for  the  companion  tree,  treated 
with  the  California  wash,  is  82  per  cent. 

Tree  No.  22. — A  peach-tree,  thirteen- feet  high,  with  a  six- 
inch  trunk  and  a  twelve-foot  spread;  in  poor  condition,  though  but 
moderately  infested.  Treated  but  once,  and  that  on  the  tenth  day 
after  the  insecticide  application,  fifteen  gallons  of  water  being 
used.  The  corresponding  tree  of  the  second  lot  was  No.  35. 
Forty-four  per  cent,  of  the  scales  alive  in  the  beginning;  88  per 


260  BULLETIN  NO.  Jl.  [Apri/, 

cent,  of  these  dead  on  the  fifth  day,  and  90  per  cent,  on  the 
thirteenth,  with  a  final  average  ratio  of  95  per  cent,  destroyed; 
this  to  be  compared  with  a  94  per  cent,  average  of  the  companion 
tree. 

Tree  No.  23. — A  fifteen-foot  apple-tree,  with  an  eight-inch 
trunk  and  a  fifteen-foot  top;  in  poor  condition,  moderately  infested. 
This,  like  32,  treated  with  three  daily  water  sprays  of  fifteen  gal- 
lons each  on  three  days  immediately  following  the  insecticide 
treatment — a  duplicate  in  this  respect  of  No.  32  of  the  second  lot. 
Forty-nine  per  cent,  of  the  scales  alive  in  the  beginning;  65  per 
cent,  of  these  dead  on  the  fourth  day  and  88  per  cent,  on  the 
thirteenth,  with  a  final  average  destruction  of  89  per  cent,  that  of 
the  companion  tree,  treated  with  the  California  wash,  being  85  per 
cent. 

Tree  Xo.  2+. — A  sixteen-foot  peach-tree,  with  a  six- inch  trunk 
and  a  nine-foot  top;  in  fair  condition,  moderately  infested. 
Treated  on  two  successive  days  immediately  following  the  insecti- 
cide application  with  fifteen  gallons  of  water  on  each  day,  the  second 
of  these  treatments  coinciding  with  the  first  day  of  rain.  Forty-two 
per  cent,  of  the  scales  alive  in  the  beginning;  38  percent,  of  these 
dead  on  the  second  day  and  92  per  cent,  on  the  fifth,  the  average 
final  result  being  the  destruction  of  93  per  cent,  of  the  scales — to 
be  compared  with  87  per  cent,  finally  destroyed  on  the  companion 
tree,  No.  33,  treated  with  the  California  wash. 

Tree  No.  26. — A  twelve-foot  peach-tree,  with  a  six-inch  trunk 
and  an  eleven-foot  top;  in  very  poor  condition  though  but  moder- 
ately infested.  Treated,  like  No.  36  of  the  second  lot,  with  fifteen 
gallons  of  water  on  the  day  following  the  insecticide  application, 
and  another  fifteen  gallons  on  the  ninth  day  thereafter,  that  is,  the 
15th  day  of  March.  This  last  treatment  coincided  with  the  third 
rainfall.  Thirty-three  per  cent,  of  the  scales  alive  at  first;  35  per 
cent,  of  these  dead  on  the  second  day,  68  per  cent,  on  the  fourth, 
84  per  cent,  on  the  fifth,  and  93  per  cent,  on  the  fifteenth— when 
the  next  succeeding  count  was  made.  A  general  final  average  of  92 
per  cent,  of  the  scales  destroyed.  The  companion  tree  of  the  second 
lot  gives  a  ratio  of  97  per  cent,  finally  killed. 

Tree  Xo.  28. — A  fourteen-foot  peach-tree,  with  a  five-inch 
trunk  and  a  ten-foot  top;  in  very  poor  condition,  though  but  mod- 
erately infested  with  the  scale.  This  tree  was  reserved  as  a  check 
upon  the  experiment,  without  water  treatment  of  any  kind,  com- 
paring in  this  respect  with  No.  20  of  Lot  2.  Fifty-eight  per  cent, 
of  the  scales  were  alive  on  it  in  the  beginning;  76  per  cent,  of 
these  were  dead  on  the  fifth  day,  and  91  per  cent,  on  the  tenth, 


I902.J  EXPERIMENTS  WITH  INSECTICIDES  FOR  THE  SAN  JOSE  SCALE.  26l 

the  final  average  destroyed  being-  91  per  cent.     The  corresponding 
ratio  for  the  companion  tree  of  the  previous  lot  was  95  per  cent. 

J^ree  No.  jo. — A  twelve-foot  apple-tree,  with  an  eight-inch 
trunk  and  a  fourteen-foot  top;  in  good  condition,  and  but  moder- 
erately  infested.  Treated  but  once,  and  that  with  thirty  gallons 
of  water  on  the  next  day  after  the  application  of  the  insecticide. 
Forty-four  per  cent,  of  the  scales  alive  in  the  beginning  ;  92  per 
cent,  of  these  found  dead  on  the  sample  examined  on  the  fifth  day 
after  treatment,  the  final  average  effect  being  the  destruction  of  89 
per  cent,  of  the  scales.  On  tree  No.  31,  corresponding  to  this  in  the 
second  lot,  the  average  final  ratio  was  84  per  cent,  destroyed. 

COMPARISON  OF  VALUES  OF  OKEGON  AND  CALIFORNIA  WASHES. 

Comparison  of  Lot  3  with  the  companion  trees  similarly  treat- 
ed in  Lot  1  brings  out  very  definitely  the  relative  advantage  of  the 
Oregon  wash.  The  general  average  of  the  ratios  of  final  destruc- 
tion is  93  per  cent,  for  the  Oregon  wash  and  87  per  cent,  for  the 
lime,  sulphur,  and  salt.  If  we  limit  the  comparison  to  the  three 
pairs  of  trees  which  received  the  water  treatment  within  the  first 
five  days  after  the  application  of  the  insecticide,  that  is,  to  Nos.  1,  2, 
and  3  of  Lot  1,  and  to  1 1,  12,  and  13  of  Lot  3,  we  find  that  in  the  latter 
94  per  cent,  of  the  scales  were  finally  killed,  and  in  the  former  only 
82  per  cent. — an  unmistakable  indication  that  the  Oregon  wash  was 
not  at  all  affected  in  these  experiments  by  water  treatment  ;  while 
the  effect  of  the  California  wash  was  considerably  reduced, — a 
clear  difference  of  12  per  cent,  of  effectiveness  in  favor  of  the 
Oregon  wash.  , 

Comparing  next  the  general  averages  of  final  effects  shown  by 
the  ratios  for  corresponding  trees  of  Lots  2  and  4,  contrasting  thus 
with  respect  to  these  two  lots  the  advantages  of  the  California 
and  the  Oregon  wash,  we  find  them  to  be  as  88  per  cent,  and  92 
per  cent,  respectively — a  difference  of  4  per  cent,  in  final  effect 
shown  by  this  group  of  experiments  in  favor  of  the  Oregon  wash. 

Bringing  together  the  two  lots  representing  each  insecticide 
treatment  and  combining  averages  for  the  two  insecticides  as  rep- 
resented by  the  four  lots  of  trees,  it  appears  that  92  per  cent,  of 
the  scales  were  destroyed  by  the  Oregon  -wash  on  fifteen  trees  as 
compared  with  87  per  cent,  on  fifteen  trees  identically  treated  after 
spraying  with  the  California  wash — a  difference  of  5  per  cent,  in 
favor  of  the  former  treatment.* 

*The  slight  difference  between  this  statement  and  the  one  on  p.  244  is  due  to 
the  fact  that  in  the  former  certain  trees  treated  with  the  California  wash  were 
included  which  were  not  exactly  duplicated  as  to  treatment  by  any  of  those  treated 
with  the  Oregon  wash. 


262  BULLETIN  NO.  Jl.  [April, 

THE  TENT  EXPERIMENT. 

All  the  preceding-  experiments  were  intended  to  test  the  ef- 
fect of  artificial  applications  of  water  on  the  action  of  the  two  in- 
secticides, these  applications  being-  made  in  a  way  to  simulate  the 
effects  of  rainfall.  They  were  interfered  with  slightly  by  the 
three  periods  of  light  rain,  the  effects  of  which  could  not  be  clear- 
ly separated  from  those  of  the  artificial  treatment. 

With  a  view  to  a  test  of  the  effects  of  rainfall,  a  small  experi- 
ment was  undertaken  in  which  two  trees — one  treated  with  the 
California  wash  and  the  other  with  the  Oregon  wash — were  cov- 
ered with  heavy  canvas  during  the  night  and  whenever  rain  threat- 
ened by  day.  Two  other  trees  were  similarly  treated  and  left 
at  all  times  exposed,  and  still  two  more,  selected  because  of  their 
close  correspondence  to  the  experimental  trees,  were  reserved  with- 
out treatment,  as  checks.  This  experiment  was  begun  March  20. 
The  trees  selected  (the  only  ones  remaining  available)  were  peach- 
trees  on  high  ground  and  light  soil,  heavily  infested,  and  in  very 
poor  condition.  The  drouth  of  the  preceding  season  had  affected 
them  very  seriously,  the  young  wood  being  largely  killed,  and  on- 
ly 29  per  cent,  of  the  young  scales  on  them  being  still  alive. 

The  weather  was  favorable  to  the  experiment.  The  insecti- 
cides were  applied  on  the  afternoon  of  March  20,  and  a  slow  fine 
rain  began  at  5  p.  m.  of  the  same  day  and  continued  until  nine 
o'clock  and  for  an  unknown  time  into  the  night,  Rain  fell  in  a  con- 
tinuous drizzle,  broken  by  showers,  the  whole  of  the  following 
day,  March  21,  to  an  amount  estimated  by  Mr.  Titus  at  more  than 
thirty  gallons  per  tree. 

The  temperature  of  the  20th  was  34°  at  7  a.  m.  and  57°  at 
noon;  that  of  the  21st  was  44°  at  7  a.  m.  and  52°  at  noon,  the 
wind  from  the  southeast  both  days.  Observations  on  this  experi- 
ment continued  only  until  the  25th,  but  counts  of  the  scales  were 
made  daily  up  to  that  time — 3,000  scales  for  the  four  experimental 
trees,  and  2,050  for  the  two  checks. 

In  thi  s  small  experiment  no  differences  of  any  significance  were 
made  out  in  the  action  of  the  insecticides,  the  total  general  effect 
being  the  destruction  of  approximately  95  per  cent,  of  the  scales, 
and  variations  from  this  average  in  the  individual  trees  being  too 
slight  to  take  into  account.  So  far  as  any  conclusion  can  be  drawn 
from  an  experiment  on  so  small  a  scale,  we  can  only  infer  that  a 
rainfall  such  as  described,  occurring  at  the  time  of  the  insecticide 
treatment,  would  have  no  appreciable  effect  on  the  action  of  either 
of  the  washes.  The  apparent  extraordinary  efficiency  of  the 


1902.]  EXPERIMENTS  WITH  INSECTICIDES  FOR  THE  SAN  JOSE  SCALE.  263 

washes  on  these  trees  is  plausibly  explained  by  Mr.  Titus  as  con- 
nected with  the  poor  condition  of  the  trees  and  the  probable  con- 
sequent low  vitality  of  such  of  the  scale  insects  as  remained  alive. 

EFFECTS  OF  RAIN  AND  WATER  SPRAYS  IN  WASHING  OFF  DEAD 

SCALES. 

Noticing-  that  many  scales  were  loosened  and  washed  away  af- 
ter insecticide  treatment  of  the  trees,  Mr.  Titus  made  some  care- 
ful counts  from  day  to  day  of  selected  lots  of  scales  on  the  experi- 
mental trees  to  determine  the  circumstances  and  the  ratio  of  their 
diminution  in  numbers.  Selecting-,  for  example,  a  definite  part  of 
a  branch,  counting-  a  hundred  scales  on  it  when  the  insecticide 
was  applied  and  marking1  the  area  occupied  by  them,  he  counted 
them  each  day  thereafter  for  several  days  and  thus  arrived  at  an 
exact  conclusion  as  to  the  effect  of  the  fluid  applications  and  the 
incidental  rains.  Thus,  on  No.  1,  300  scales  counted  March 
3  were  reduced  to  188  by  March  15 — a  loss  of  37  per  cent.  On 
No.  11,  400  scales  were  reduced  in  the  same  time  to  223 — a  loss 
of  22  per  cent.  Both  these  trees,  it  will  be  remembered,  were 
sprayed  with  the  insecticide  March  3,  and  daily  thereafter  for  one 
week  with  fifteen  g-allons  of  water.  On  No.  3,  100  scales 
were  reduced  in  eight  days  to  72 — a  loss  of  28  per  cent.,  this  tree 
having-  been  three  times  sprayed,  with  fifteen  gallons  of  water 
each  time.  On  No.  6,  sprayed  once  with  thirty  g-allons.  the 
loss  was  25  per  cent,  in  eight  days;  and  on  No.  14,  receiving- 
the  same  treatment  except  that  the  insecticide  used  was  the  Ore- 
gon instead  of  the  California  wash,  the  loss  for  the  same  period 
was  11  per  cent.  No.  21,  sprayed  also  but  once,  with  15  g-allons 
of  water,  lost  20  per  cent,  of  its  scales  in  seven  days;  No.  42, 
exposed  to  rains  for  a  day  and  a  nig-ht,  lost  in  five  days  11  per  cent, 
of  its  scales;  and  No.  43,  similarly  exposed,  lost  15  per  cent. 

The  check  trees  40  and  41,  on  the  other  hand,  kept  without 
treatment  of  any  kind,  lost  within  five  days  but  four  scales  out  of 
five  hundred  counted. 

It  was  further  apparent  from  observations  made  in  the  field 
that  a  brief  but  hard  and  dashing-  rain  would  detach  many  more 
scales  than  a  light  rain  longer  continued  and  that  a  fine  misty 
rain  did  not  loosen  the  scales  at  all. 

PRACTICAL  CONCLUSIONS. 

The  foreg-oing-  described  observations  and  experiments  gx>  to 
show  that  the  Oregon  wash  of  lime,  sulphur,  and  blue  vitriol,  pre- 
pared as  described  on  p.  246,  is  a  valuable  insecticide  for  winter 


264  BULLETIN  NO.  Jl.  [April, 

use  in  the  climate  of  Illinois  for  the  destruction  of  the  San  Jose 
scale;  that  its  full  effect  will  be  produced  in  about  a  week;  and  that 
frequent  short  rains  will  not  noticeably  diminish  or  delay  its  ac- 
tion, even  when  they  come  within  the  first  five  days  after  the  in- 
secticide treatment.  It  is  entirely  harmless  to  any  leafless  tree, 
and  hence  may  be  freely  used  in  winter  (but  in  winter  only)  for  all 
kinds  of  trees,  shrubs,  and  vines. 

The  California  wash  of  lime,  sulphur,  and  salt,  prepared  as 
described  on  p.  246,  is  a  little  less  effective  than  the  Oregon  wash 
as  a  scale  destroyer,  and  is  considerably  more  likely  to  deteriorate 
after  application  if  exposed  to  rains  within  the  first  few  days. 
Otherwise  its  effects  and  characteristics  are  very  similar  to  those 
of  the  Oregon  wash, 

It  should  be  generally  known  that  both  these  washes  corrode 
brass  and  copper  rapidly,  and  that  consequently  an  iron  pump  may 
be  used  to  better  advantage  in  spraying-  them  than  one  made  in  part 
of  brass. 

With  respect  to  the  comparative  effectiveness  of  these  washes 
and  the  better  known  whale-oil  soap  and  coal-oil  mixtures  we  have 
as  yet  no  accurate  knowledge.  There  is  nothing  to  indicate,  how- 
ever, that  the  former  are  less  effective  here  than  on  the  Pacific 
Coast,  where  they  seem  to  have  been  found  very  satisfactory  in  the 
hands  of  the  ordinary  orchardist  for  the  destruction  of  the  San 
Jose  scale.  Over  both  the  latter  applications  they  have  the  very 
great  advantage  that  they  are  harmless  to  the  tree,  and  that  they 
do  not  endanger  the  crop  of  the  following  year.  They  are  also  de- 
cidedly cheaper  than  either  the  whale-oil  soap  or  the  kerosene  emul- 
sion. In  our  winter's  work  the  cost  of  the  materials  for  these  various 
mixtures  has  been  $1.12  per  hundred  gallons  of  the  Oregon  and  the 
California  washes  ;  $2.80  per  hundred  gallons  of  kerosene  emul- 
sion, diluted  to  contain  twenty  per  cent,  of  kerosene  ;  and  $6.50  for 
the  same  quantity  of  the  whale-oil  soap  solution,  at  the  usual 
strength  of  two  pounds  to  the  gallon  of  water. 


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